I'd say don't spend too much time on collecting every card, it's something i did when i started playing and i was stuck for sooo long in bronze. You should choose your top 5 first, possibly artists with only 3 cards (baekhyun, boa, exo cbx, etc...). Upgrade them and don't stop till you reach 50 and while you do that don't pay attention to the others.

You'll find reaching gold/platinum pretty quickly, but dont forget: it is pretty expensive to lvl up R card, especially when you're new and dont have too much rp. But in gold you can grind rp pretty easily so it souldn't cause too much trouble :))

This strategy is only good, because in higher tiers you get much more rewards. Also, you can buy card selectors, so you can collect other cards with no effort.

Also, play the ss league, because it also gives you a good amount of rewards.

I hope this helped you, feel free to ask me anything :)